<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *{
            padding: 0;
            margin: 0;
        }
        html,body{
            background-color:rgba(106, 235, 74, 0.664);
        }
        header{
            width: 500px;
            height: 600px;
            margin: 50px auto;
            background-color: :rgba(106, 235, 74, 0.664);
        }
    </style>
</head>
<body>
    <header></header>
</body>
</html>